1. Field of Invention
The present invention relates to a safe delivery system of agriculturally active material and a process for preparing microencapsulated suspension of agriculturally active material, preferably including pyrethroids wherein the encapsulating agent is a graft copolymer of a starch and at least one vinyl monomer.
2. Description of Related Art
In the agrochemical industry, insecticides are formulated as dust, emulsifiable concentrates, suspension concentrates, wettable powders or wettable granules, and water dispersible granules depending on the properties of the active ingredient and the target pest species and market. Insecticides such as lambda cyhalothrin, cypermethrin, fenvalerate, permethrin, alpha-cypermethrin, and similar compounds, which are moderately toxic in the technical form, have a high skin irritant property and in some cases may provoke an adverse skin reaction such as burning, tingling, numbness or prickling sensation., also generally known as paraesthesia. These skin irritant properties are most pronounced in the areas of an operator's face, hand, and neck during application of these insecticides. For delivering such agriculturally active materials to a target, encapsulation or microencapsulation is one of the safest modes. Encapsulation, or more specifically microencapsulation, is increasingly being used to target specific insects, as it also provides a safer handling of toxic fungicides and insecticides. A microcapsule is a 10−3 m to 10−9 m diameter particle, composed of an inner core material and an outer shell. Microencapsulation of these kinds of agrochemicals can also be advantageous in providing the active material in relatively more concentrated form than the emulsifiable concentrate, wettable powder etc., at the same time reducing the amount of other ingredients such as surfactants, solvents, dye(s) etc.
Microencapsulation of a number of different agriculturally active materials and pesticides has been known for many years by using various processes or techniques for microencapsulation. The general technology for forming microcapsules is divided into two classifications known as physical methods and chemical methods. The physical methods are spray coating, spray drying, pan coating, rotary disk atomization etc. The chemical microencapsulation methods are phase separation, interfacial polymerization, simple and complex coacervation method etc.
The total process of microencapsulation covers three separate steps on a time scale. The first step consists of forming a shell around a core material. The second step involves keeping the core inside the shell material so that it does not release. Also, the shell material must prevent the entrance of undesirable materials that may harm the core. And finally, it is necessary to release the core material beginning at the right time, stage and at the right rate.
Prior encapsulation methods include a process for the preparation of microencapsulated water-immiscible material, including pesticides and other agrochemicals, by interfacial polymerization techniques using one or more polyisocyanates and producing microcapsules having a droplet size of from 0.5 to about 4000 microns, which provides a controlled or sustained release (over weeks) of the active ingredients. This type of controlled released encapsulation is useful in the case of soil application. Whereas, fast release is required in the case of foliar applications.
Another encapsulation method includes a process of encapsulation of a water-immiscible material. i.e. pyrethroid insecticide, within discreet capsules of polyurea prepared from an aromatic diisocyanate. However, the untreated isocyanate, if any, of said isocyanates may cause skin/eye irritation due to its high toxicity
Release rates are governed by the capsule particle size, the thickness of the wall and the permeability of the wall. Small particles with thin walls and low cross-linking density allow the fastest possible release.
Starch is a cheap and natural polymer and is a renewable degradable carbohydrate biopolymer that can be taken from various sources by environmentally sound processes. Starch is hydrophilic and a partially water soluble polymer. Starch-based biodegradable low-density polyethylene (LDPE) films have been used for graft copolymerization of vinyl acetate with ceric ammonium nitrate. Additionally, it is known to graft vinyl acetate and starch acetate with a high degrees of substitution copolymerized to prepare a kind of biodegradable material.